The present invention relates to an electrically erasable and programmable nonvolatile semiconductor memory device such as an EEPROM (Electrically Erasable and Programmable Read Only Memory) and, more particularly, to a nonvolatile semiconductor memory device capable of high-speed rewrite processing.
A microcomputer incorporating an EEPROM conventionally rewrites data at an arbitrary address in the EEPROM by erasing and writing data in units of addresses.
A conventional EEPROM write operation will be explained with reference to FIGS. 5A to 5F. Data at a plurality of addresses, e.g., addresses 0 and 1 in the EEPROM can only be rewritten by two rewrite operations (one rewrite operation includes a pair of erase and write) of address 0 at time t4 and address 1 at time t5, as shown in FIGS. 5D, 5E, and 5F.
In a microcomputer incorporating a large-capacity EEPROM, the number of EEPROM rewrite operations is large, and thus the rewrite time for one operation must be suppressed as short as possible.
However, the EEPROM rewrite time is much longer than the normal machine cycle of the microcomputer, so the EEPROM rewrite time is very long in the microcomputer incorporating the conventional EEPROM.